Background. Adolescence represents a critical period for the development of overweight that tracks into adulthood. This risk is significantly heightened for teens that become pregnant each year and experience postpartum weight retention and overweight leading to impaired glucose tolerance, type 2 diabetes, and other diseases. The postpartum period offers a window of opportunity to modify eating and activity patterns associated with obesity. Aims. The primary aim of our proposal is to test Balance Adolescent Lifestyle Activities and Nutrition Choices for Energy (BALANCE), a multilevel intervention designed to reduce overweight in postpartum teens, as measured by change in Body Mass Index (BMI). A series of secondary aims will then examine whether all or part of improvements in BMI can be explained by changes in adolescent behavior through replacement of 'obesogenic' patterns (soda, high fat snack intake, excess portion size, and sedentary activity) with 'energy' patterns (low fat milk/water consumption, FV intake, appropriate portion size, and walking), and by improvements in knowledge, modeling, and social support. This study will be conducted in collaboration with Parents As Teachers (PAT), a national parent education organization located in over 3108 PAT-affiliated sites across all 50 states. Methods and Evaluation. BALANCE reflects an ecological approach that recognizes the multiple, protective, and interactive influences on the teen (peers, parent educators) with behavior change strategies based on social cognitive theory. The study will take place within the multiple settings where teens spend time and will be implemented through personal visits by parent educators in the home, classroom-based activities with peers at school, and Internet- based interactions with parent educators and peers across the country. A group randomized, nested cohort design will be used to evaluate the impact of the program on the BMI of the overweight postpartum adolescent randomized to either a control (n=945) group receiving the standard PAT program, or intervention (n=945) group receiving BALANCE. Innovation: This innovative proposal is the first of its kind to (1) prevent or reduce the development of long-term overweight among high risk postpartum teens; (2) test a diet and activity intervention that combines one-to-one personal mentoring at home with group intervention in the classroom setting plus Internet activities supporting both approaches; and (3) secure a foundation for disseminating an empirically tested intervention to 26,000 teen parents located in PAT sites across the nation.